1. Field of the Invention
Embodiments of the present invention relate to semiconductor memory devices and methods of forming the same. More particularly, embodiments of the present invention relate to phase change memory devices and methods of forming the phase change memory devices.
2. Description of the Related Art
Phase change memory devices are non-volatile memory devices, i.e., memory devices that retain stored data even when power supplies are interrupted. A unit cell of a phase change memory device may include a phase change material as an element for storing data.
The phase change material may have a different resistivity corresponding to each material state, i.e., phase. For example, a phase change material at an amorphous state may have a higher resistivity than the phase change material at a crystalline state. Accordingly, logic “1” data or logic “0” data may be stored in the phase change material using different resistivities according to the material state.
The phase change material may change to an amorphous state or to a crystalline state by controlling heat applied to the phase change material, e.g., heat in terms of temperature and/or duration. For example, a phase change material may change to an amorphous state from a crystalline state by applying heat corresponding to a melting point temperature of the material, followed by a quick cooling of the phase change material. Alternatively, the phase change material may change to a crystalline state from an amorphous state by applying heat corresponding to a crystallization temperature of the material, i.e., a temperature lower than a melting point temperature, followed by a slow cooling of the phase change material.
A conventional heat source of the phase change material may be, e.g., current applied to the phase change material, so temperature and duration of the heat applied to the phase change material may be controlled by adjusting an amount of the current. For example, the amount of current applied to the phase change material may be increased in order to increase temperature. An increase in the amount of current, however, may increase power consumption and decrease an integration degree of the conventional phase change memory device.